Method for producing a cooled, lost-wax cast part

ABSTRACT

The invention relates to a method for producing a cooled cast part ( 1 ) for a thermal turbo machine by using a known casting process. Between a wax model ( 10 ) of the cast part ( 1 ) and a ceramic core ( 6 ), a wax seal ( 8 ) is applied by hand above a step ( 7 ), only on an additional shoulder ( 9 ). The material that is created during the casting process at this point by the shoulder ( 9 ) and the wax seal ( 8 ) can be ground off without causing rough areas on the step ( 7 ) to form. This simplifies the welding or soldering of a cooling plate to the step ( 7 ).

FIELD OF THE INVENTION

[0001] The invention relates to a method for producing a cooled castpart produced by a lost-wax process for a thermal turbo machineaccording to the preamble of claim 1.

BACKGROUND OF THE INVENTION

[0002] Cast parts for thermal turbo machines are produced using knowncasting processes. Casting furnaces for such casting processes areknown, for example, from publications EP-A1-749 790, U.S. Pat. No.3,763,926, or U.S. Pat. No. 3,690,367. The casting molds usually areprovided in the form of a wax model. A process for producing a complexpart of a gas turbine using a casting mold is known, for example, frompublication U.S. Pat. No. 5,296,308.

[0003] Depending on the specific embodiment, a core is placed into thewax model. This core contains the structure of the cavity that forms aspecific cooling structure inside the casting part. In these castingparts, a wax seal must be applied between the wax model and the core inorder to prevent the slip, that in its dry form forms the casting mold,from penetrating into the intermediate space. The wax seal is applied byhand onto a step adjoining the core. This step has the ultimate purposeof holding a cooling plate. The cooling plate is soldered or welded ontothe step and is used, by means of cooling holes, for impact-cooling theplatform located below it. In order to prevent leakages of cooling air,the surface of this step should be smooth. But this is in contradictionwith the applied wax seal that, after casting, results in anaccumulation of material above the step. In order to get closer to thegoal of a smooth surface of the step, an additional process step, forexample grinding or eroding, is necessary.

SUMMARY OF THE INVENTION

[0004] The invention is based on the objective of creating a method forproducing a thermally loaded and cooled cast part for a thermal turbomachine by using a known casting process, whereby the casting mold ofthe cast part is produced with a wax model and a ceramic core, and thesubsequent production steps are simplified and optimized.

[0005] According to the invention, this objective is realized with amethod according to the preamble of Claim 1 in that, prior to theproduction of the casting mold of the cast part between the wax modeland the core, the wax seal is applied to only one shoulder that islocated above the step in the direction towards the side of the core.

[0006] This provides the advantage that even during the casting processit can already be prevented that rough areas are created on the stepthat would result in a leakage of the cooling air at the cooling plate.The material that is created during the casting process as a result ofthe wax seal and the shoulder can be ground off or removed using anotherappropriate manner with a uniform process step without forming roughareas on the step. A cooling plate can be soldered to this step withoutany additional process steps.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] The invention is described in reference to the enclosed drawings,whereby

[0008]FIG. 1 shows a model of a turbine blade,

[0009]FIG. 2 shows a section through a turbine blade according to theinvention along to line II-II in FIG. 1, and

[0010]FIG. 3 shows a section through a turbine blade according to theinvention along line II-II in FIG. 1 after a successful casting process.

[0011] Only those elements essential to the invention are shown.Identical elements are designated with the same reference characters inthe different drawings.

DETAILED DESCRIPTION OF THE INVENTION

[0012] The invention relates to a method for producing a thermallyloaded and cooled lost-wax cast part for a thermal turbo machine. Inparticular, this may be, for example, a guide or rotating blade, orother cooled rotor or stator segments of a gas turbine or compressor.These cast parts and the method according to the invention for theirproduction are explained in more detail below in reference to theenclosed figures.

[0013] The cast parts are produced using casting furnaces knowngenerally from the state of the art. By using such casting furnaces,complex components that can be subjected to high thermal and mechanicalloads can be created. Depending on the process conditions, it is herebypossible to produce the cast body in a directionally solidified manner.It can hereby be constructed as a single crystal (SX) orpolycrystalline, as fringe crystals that have a preferred direction(“directionally solidified”, DS). It is especially important that thedirectional solidification takes place under conditions at which anintensive heat-exchange takes place between a cooled part of a castingmold holding a molten starting material and the still molten startingmaterial. This permits the formation of a zone of directionallysolidified material with a solidification front that, when the heat iscontinuously withdrawn, migrates through the casting mold while formingthe directionally solidified cast part.

[0014] Publication EP-A1-749 790, for example, discloses such a processand apparatus for producing a directionally solidified cast part. Theapparatus comprises a vacuum chamber that contains an upper heatingchamber and a lower cooling chamber. The two chambers are separated fromeach other by a baffle. The vacuum chamber accepts a casting mold thatis filled with a molten mass. In order to produce thermally andmechanically loadable parts, such as guide or rotating blades for gasturbines, a super-alloy based on nickel can be used, for example. Thebaffle is provided in the center with an opening through which thecasting mold is moved slowly during the process from the heating chamberto the cooling chamber, so that the cast part directionally solidifiesfrom the top to the bottom. The downward movement is brought about witha drive rod on which the casting mold is positioned. The bottom of thecasting mold is constructed with water cooling. Below the baffle, meansfor generating and guiding a gas stream are provided. Through the gasstream next to the lower cooling chamber, these means ensure additionalcooling and therefore a greater temperature gradient at thesolidification front.

[0015] A similar process, which in addition to the heating and coolingchamber works with an additional gas cooler, is also known, for example,from U.S. Pat. No. 3,690,367.

[0016] Another process for producing a directionally solidified castpart is known from publication U.S. Pat. No. 3,763,926. In this process,a casting mold filled with a molten alloy is immersed continuously intoa bath heated to approximately 260° C. This achieves a particularlyrapid removal of heat from the casting mold. This and other, similarprocesses are known under the name of LMC (liquid metal cooling).

[0017] For the invention, it is advantageous, that this type of castingfurnaces is used for producing monocrystalline or directionallysolidified cast parts, but it is not limited to this. In principle, thesolidification also can take place non-directionally.

[0018]FIG. 1 shows a wax model 10 of a cast part 1, for example aturbine blade to be cast. The turbine blade is provided with a platform2, a blade vane 3, and blade tip 2. This wax model 10 then is immersedinto a liquid, ceramic material, also called a slip. Hereby the latercasting mold of cast part 1 is formed around the wax model 10. Theceramic model is then dried so that the casting mold with which the castpart 1 is produced is created. After the slip is dried, the wax isremoved using a suitable heat treatment, i.e. is burnt away. During theprocess step, the casting mold is also fired, i.e. it receives itsstrength in this way. The cast part 1 is produced in a known manner withthe casting mold created in this way by using a known casting furnacethat was described in more detail above. The ceramic casting mold andthe core are later removed in an appropriate manner, for example byusing a strong acid or base.

[0019] The turbine blade of FIG. 1 has a cavity into which cooling airis passed during the operation of the turbo machine. This cooling air isable to leave the finished turbine blade again through cooling holes 5.As seen in FIG. 1, a ceramic core 6 that reflects the internal geometryof the cavity is provided during the production process of the castingmold in the later cavity of the wax model 10. In the shown turbineblade, the platform 2 is cooled additionally by impact cooling. Hereby acooling plate 11 provided with cooling holes 12 is soldered or welded toa step 7 next to the ceramic core 6 and on the edge of the platform 2 inthis cast component. This cooling plate 11 is described in more detailin reference to FIG. 3.

[0020] Prior to the production of the casting mold, a wax seal 8 ismanually provided between the ceramic core 6 and shoulder 9. This waxseal 8 has the objective of preventing the undesired penetration of slipinto the inner chamber of the ceramic core 6.

[0021]FIG. 2 shows a section along line II-II of FIG. 1 that extendsthrough the step 7, the wax seal 8, and through the ceramic core 6.According to the invention, the wax seal 8 is provided only on ashoulder 9 located above the step 7 towards the ceramic core 6. Thisprocess results in two advantages. During the casting process, the step7 and wax seal 8 create additional, cast material on the turbine blade.As seen in FIG. 3, this material has a specific height s and can bemachined, i.e. ground off, independently from step 7 or independentlyfrom the surface of step 7. This uniform process step also may beperformed by erosion. In spite of this additional process step, the step7 to which the cooling plate 11 is soldered remains unaffected, which inany case ensures a smooth surface of the step 7. The cooling air 13penetrates through the cooling holes 12 and in this way is able to coolthe platform 2 by impact cooling. The smooth surface of the step 7 isimportant since even small rough areas could reduce the cooling effectof this impact cooling as a result of leakage losses. Another advantageis that the existing shoulder 9 prevents the liquid solder thatdistributes itself over the entire step 7 from flowing into the cavityof the cast part 1. Since during the operation of the cast part aninsert will be located in its cavity also, it is important that nosolder adheres to this insert and thus adversely affects its properfunction.

What is claimed is:
 1. Method for producing a cooled cast part (1) for athermal turbo machine by using a known casting process, whereby thecooled cast part (1) is produced by means of a casting mold, wherebythis casting mold is produced by using a wax model (10) and a core (6)located inside the wax model (10), hereby immediately next to the core(6) is located a step (7) for the attachment of a cooling plate (11) tothe finished cast part (1), and whereby prior to the production of thecasting mold a wax seal (8) is applied by hand between the core (6) andthe wax model (10), characterized in that prior to the production of thecasting mold of the cast part (1) between the wax model (10) and thecore (6), the wax seal (8) is applied only to a shoulder (9) that islocated above the step (7) in the direction towards the side of the core(6).
 2. Method as claimed in claim 1, characterized in that after thecasting process, the material on the cast part (1) that is located atthe point of the shoulder (9) and the wax seal (8) is partially groundoff or eroded, whereby the step (7) is not affected by this processstep.
 3. Method as claimed in claim 2, characterized in that the coolingplate (11), in which cooling holes (12) are located, is solder or weldedto the surface of the step (7).
 4. Method as claimed in one of theprevious claims, characterized in that a casting process for producingmonocrystalline, directionally or non-directionally solidified is used.5. Method as claimed in one of previous claims, characterized in that itis a method for producing a guide or rotating blade of a gas turbine ora compressor with impact cooling of the platform (2).